With a diet significantly made of sugary nectar, you might have wondered why hummingbirds don’t get diabetes – or do they get diabetes?
When talking about diabetes in this context, we’re talking specifically about type 2 diabetes where the body stops responding efficiently to insulin.
While hummingbirds consume a lot of nectar and have very high blood sugar levels, there are systems in place that help prevent hummingbirds from getting diabetes. Some of these include their energetic lifestyle, certain genes, liver efficiency and possibly red blood cell turnover rate.
If you were interested in this topic, you’re not the only one! Scientists have spent years uncovering this mystery, and so far, they’re still trying to figure it out. But in the last 3-4 decades, they have uncovered a lot.
Not only is this a topic researchers are trying to solve, there are a lot of other things about a hummingbird’s metabolism that work for their lifestyle but would kill a human or mammal. For instance, with a diet substantially composed of nectar, hummingbirds also ingest a large volume of water for their body weight, and yes – there is a such thing as too much water in organisms where too much can be really harmful.
Fortunately, because this topic may have connections to human health issues, researchers are still conducting studies to really understand the mechanisms involved and how they work in a way that seemingly prevents hummingbirds from developing insulin resistance and diabetes in the traditional sense.
Before diving into what prevents hummingbirds from getting diabetes, we need to look at how much sugar they consume and how high their blood sugar levels actually are.
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Hummingbird Blood Sugar and Sugar Consumption
On average, hummingbirds will visit feeders or flowers for nectar every 20 minutes (this is an average, not necessarily continuous). During each visit, they’ll consume between 50-200 microliters of nectar.
That amount is very small, and to help visualize it, here is a photograph of how much that would be using a quarter as a reference point.
Each day, they’ll drink 1-2 times their body weight in nectar – flower nectar has a range of 20-30% sugar concentration.
Just take a moment to imagine drinking 1-2 times YOUR body weight in any kind of drink – it’s a lot!
Interestingly, researchers found hummingbirds have very high blood glucose (blood sugar) levels.
During the day, while feeding on nectar, hummingbirds can have blood glucose levels of 42 millimoles or 740 milligrams per deciliter.
When they’re not drinking nectar (fasting) scientists discovered blood glucose levels of about 17 millimoles or about 300 milligrams per deciliter.
These amounts might not be all that meaningful until we look at what a healthy blood sugar level is in a nondiabetic adult, which is 70-99 milligrams per deciliter.
So when a hummingbird is fasting, this teeny tiny bird still has about 3 times the blood sugar levels of a nondiabetic human adult! It’s still really high.
How do they survive it? Let’s take a look at some of the different factors involved in bird metabolisms that may enable hummingbirds to withstand significantly high sugar intake.
1. A hummingbird’s energy expensive lifestyle
One of the first reasons that might come to mind about why hummingbirds really don’t seem to develop diabetes is because of their exercise. But for hummingbirds, their intense movement is a way of life.
Their lifestyle could be seen as energy expensive.
If you’ve ever watched hummingbirds, you’ll notice they don’t sit still for very long. At feeders, they usually buzz around, in and out. And while they’ll sometimes perch at feeders to drink, in wild areas where they drink nectar from flowers, they hover feed.
Hover feeding means hummingbirds don’t perch on anything while they feed on nectar. Instead, they hover over a flower, stay in position in the air while eating and beating their wings incredibly fast.
To summarize a hummingbird’s intense lifestyle compared to a person’s, we’ve created the table below:
| Hummingbird | Human | |
| Heartrate | 1200 beats/min. | 60-100 beats/min. |
| Breaths / Min. | 250 | 12-18 |
| Wing Beats | 50 | X |
Fortunately, hummingbirds break down sugars and fats into useable energy products faster than any most or perhaps any other vertebrate.
And while an energy intense lifestyle and fast metabolism is definitely a factor in reducing the risk of developing type 2 diabetes, with hummingbirds, their energy consumption almost requires significant sugar consumption to pay for the amount of energy they use.
But, something important to keep in mind about all of this is that even though they move very fast and continuously hovering as they feed, the measure of blood sugar or blood glucose is still very high.
Their blood sugar levels only start to drop when they go into a fasting state at night or during periods where they aren’t feeding, and even at that fasting state, they have a blood sugar level 3 times higher than a nondiabetic person.
So that means, there has to be a lot of other things happening in their body to help them withstand all this sugar.
2. Vitamin C production in birds
Unlike humans, birds can produce vitamin C in their bodies. This is very important because vitamin C reduces a process called glycation.
Glycation occurs when sugars attach to a protein, lipid or nucleic acid (DNA or RNA). But in this context, we’ll focus on a sugar’s bond to proteins.
Researchers found glycation may play a role in certain diseases, diabetes being one of them.
Let’s look at a familiar protein – hemoglobin. Millions of hemoglobin proteins are found in one single red blood cell and this protein is responsible for transporting oxygen.
Sugar can bind to hemoglobin, and when a hemoglobin protein is bound to a sugar, it is called a glycated hemoglobin.
The A1c test used to diagnose prediabetes or diabetes measures the percentage of glycated hemoglobin
What’s fascinating with hummingbirds is that they while they have high blood sugar, even while fasting, they have lower levels of glycated hemoglobin or A1c (below what would be classically diagnosed as diabetic).
With vitamin C being shown to reduce glycation events by reversibly binding (temporarily binding) to sites where glycation could occur, vitamin C production in birds may be one reason why birds can manage higher blood sugar levels while not having such high A1c.
To summarize this idea, glucose can bind to hemoglobin and other proteins in the body, and the measure of hemoglobin bound to glucose is a test used to diagnose diabetes. However, hummingbirds have lower A1c levels, and this may be due to the protective nature of the vitamin C they produce internally.
While this might be part of the story, vitamin C production is not the whole story. And we know this because a lot of other animals, including many mammals produce vitamin C but still develop diabetes and have higher A1c.
3. Red Blood Cell Turnover Rate
Now that we’ve discussed glycated proteins, we can use those concepts to better understand how red blood cell turnover rate may be involved in diabetes prevention in hummingbirds.
First, it’s important to clarify that red blood cell turnover rate being a preventative factor is a hypothesis. Researchers will still need to conduct more studies to have better evidence of this.
But the idea is this: red blood cells in birds have an average lifespan of 20 days. In humans, however, the average red blood cell lifespan is about 120 days.
For birds, that means there are only about 20 days available for hemoglobin proteins in red blood cells to become glycated before that cell is broken down. Humans, in contrast, have a longer amount of time for hemoglobin to become glycated.
Once hemoglobin proteins are glycated, they only go away when the red blood cell itself is broken down and out of circulation.
Again, researchers are still trying to understand the connections between red blood cell turnover rate and diabetes. But we do know that there is a relationship between aging, chronic diseases and glycated molecules in the body. So it stands to reason that there might be something behind cells with glycated proteins being flushed from the body faster reducing the risk of disease.
4. Genes and glucose transport
One study found 39 genes contribute and support a hummingbird’s nectar-based life. And let’s just say too, that while hummingbirds eat bugs and have sometimes even been spotted at suet feeders, a large portion of their diet is from nectar.
A set of genes particularly interesting to researchers are the ones that encode different glucose transport proteins.
These glucose transport proteins are sort of like the gatekeepers for glucose and fructose to enter cells.
When a hummingbird fasts (sleeping, migrating or just flying and not feeding for a longer period), their bodies stop producing as many of these types of proteins, which may help maintain their blood sugar levels while they’re not feeding on nectar.
While scientists are still trying to unravel how glucose transport proteins work in birds compared to humans and other animals, it appears that the slight genetic differences in the bird version of these proteins help better regulate blood sugar as well as help regulate how sugar is used as fuel in the body.
5. Birds have higher insulin sensitivity
Insulin is released from the pancreas in our bodies, and it signals to the cells that it’s time to open those gates and let glucose in.
For people who begin developing insulin resistance, the signal is released, but the cells have a harder time registering that signal, and sugar starts to build up in the bloodstream.
Birds, however, have been found to have better sensitivity to insulin, which means their cells are able to use sugars more efficiently.
6. Sugar to fat conversion in the liver
When it comes to a hummingbird’s metabolism, the liver is very important because it is the place where sugar is converted to fat, and for hummingbirds, they do this incredibly fast.
The reason this process is so important for hummingbirds is because fat becomes their energy source when they’re not feeding.
Imagine you want to save energy in your house. You turn off all the lights, you even turn off the air conditioner. You unplug a lot of your devices, but one thing you need to keep running is your refrigerator. So some energy is still being used.
Likewise, even when hummingbirds aren’t buzzing around during the day and are sleeping at night, their bodies and the systems within require some energy – and for that, they use stored fat.
Most of the stored fat comes from sugar that has been converted to fat from the liver and adipose tissue.
The ability for hummingbirds to convert excess sugar into fat is especially important for their long migration where food is scarce, especially while crossing the Gulf of Mexico.
In the end, while these 6 factors are thought by researchers to minimize the risk of hummingbirds developing diabetes, how their bodies support a nectar-based life is still greatly unsolved. Furthermore, independently, none of these factors prevent the development of diabetes.
Instead, it is the interplay between these factors, unknown factors, and the overall unique hummingbird metabolism that may prevent hummingbirds from developing type 2 diabetes.
But because we have been inspired by how different, unique processes in other animals create better health outcomes, researchers are still trying to learn more from a hummingbird’s metabolism and biochemistry, as well as from other animals.
For now, understanding these processes in hummingbirds may help us appreciate how incredible these birds really are – for such a small bird, their bodies are incredibly optimized to help them survive some wild extremes.
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